Haaland maintained his red-hot form with a brace as Dortmund defeated visiting Union Berlin – the 21 year-old becoming the youngest player in history to reach 47 Bundesliga goals in just his 48th appearance.
After Dortmund full-back Raphael Guerreiro opened the scoring in stunning fashion, Haaland doubled Dortmund's lead in the 24th minute via a header.
A Marvin Friedrich own goal seven minutes into the second half virtually put the result beyond doubt, though Max Kruse's penalty gave Union Berlin some hope.
After Andreas Voglsmanner netted a second for Union Berlin, Haaland then produced a stunning lob over Andreas Luthe with seven minutes remaining.
"Did he really score a header today?" German star Hummels told DAZN. "He's been practising a lot.
"He's got so many strengths, now he's also working on his weaknesses.
"When he came to Dortmund from Salzburg [in 2020], his aerial game was pretty bad. [Former head coach] Edin [Terzic], Erling and I spent a lot of time practising crosses, over and over again, and now you can see where that gets you.
"He's definitely going to get 10 more goals a season because of the fact he's improved his aerial game. He's just a goalscoring machine."
Haaland has 68 goals in 67 competitive games overall for Dortmund, including 11 in eight this season.
Hummels added: "Whenever he sees a chance to put the ball in the back of the net, his eyes light up. He's going to be one of the best forwards in the world for the next 15 years."
Haaland has already scored two headers in the Bundesliga this season, as many as he managed in all of 2020-21.
"If Erling scores those headers permanently now, then 'Wow!' and 'Congratulations!' to our upcoming opponents," said Dortmund head coach Marco Rose.
Rose's Dortmund scored for a 37th consecutive Bundesliga game, a club record and the third longest such run in the league's history.
Dortmund is third in the league – a point adrift of champion and leader Bayern Munich after five rounds.